IN PICTURES | Chaos erupts as pro-Trump protesters storm US Capitol

Protesters supporting Donald Trump swarmed the US Capitol on Wednesday, putting it on lockdown, as Vice-President Mike Pence rebuffed the president's demand to overturn his loss to Democrat Joe Biden and the Senate's Republican leader denounced a bid in Congress to undo the election outcome.

On the same day a runoff election in Georgia looked set to put control of Congress in Democratic hands, Trump supporters overturned barricades and clashed with police on the US Capitol grounds and streamed inside the building.

The demonstrations flared as lawmakers met inside to formally certify Biden's victory over Trump in the November 3 election. Law enforcement authorities struggled to maintain order.

Police in the US Capitol on Wednesday responded with drawn guns and teargas as hundreds of protesters stormed the building and sought to force Congress to undo President Donald Trump's election loss shortly after some of Trump's fellow Republicans launched a last-ditch effort to throw out the results.

Members of the House of Representatives and the Senate were evacuated after pro-Trump protesters marched through the halls of Congress, forcing both chambers to suspend deliberations as they were meeting to certify President-elect Joe Biden's victory in the November 3 election.

One protester occupied the Senate dais and yelled, “Trump won that election.”

Protesters overturned barricades and clashed with police as thousands descended on the Capitol grounds. Videos showed protesters breaking windows and police deploying teargas inside the building.

Local media reported that one person had been shot and videos showed a person being wheeled from the building on a stretcher.

Pence, who had presided over the joint session of Congress, had already been escorted from the Senate.

The chaotic scenes unfolded after Trump, who is due to leave office on January 20, addressed thousands of protesters, repeating false claims that the election was stolen from him due to widespread election fraud and irregularities. Lawmakers had been debating a last-ditch effort by pro-Trump lawmakers to challenge the results, an effort that was unlikely to succeed.

Capitol police told lawmakers in the House chamber to take gas masks from beneath their seats and prepare to put them on. Officers at the front door of the House chamber had their guns drawn as someone attempted to enter the chamber.

Officers ordered people in the chamber to drop to the floor for their safety. Several hundred House members, staff and press were evacuated to an undisclosed location and were told not to leave.

Election officials of both parties and independent observers have said there was no significant fraud in the November 3 contest, which Biden won by more than 7 million votes in the national popular vote.

Weeks have passed since the states completed certifying that Biden, a Democrat, won the election by 306 Electoral College votes to Trump's 232. Trump's extraordinary challenges to Biden's victory have been rejected by courts across the country.

— Reuters